Water soaking of rayon cakes



Patented July 28, 1953 WATER SOAKING OF RAYON CAKES BEFORE CENTRIFUGAL WASHING Edward Doud, Richland, Wash., assignor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application April 14, 1949,

Serial No. 87,580

This invention relates to the centrifugal washing and purification of bucket cakes of viscose rayon yarn.

In U. S. Patent 2,243,000 there is mentioned a method of washing and purifying bucket cakes centrifugally which briefly comprises taking an acid cake as it comes from the spinning :bucket, deforming it to reduce its diameter a few per cent and then washing and purifying it in a perforated bucket of smaller diameter than the spinning bucket. By this method of washing and purifying, excess yardage is provided at the outside of the cake so that when shrinkage tendencies arise during washing and purification and later on in drying, shrinkage can take place without setting up undesirable high tensions in the yarn whether it be on the outside of the cake, on the inside of the cake or in any location therebetween. After washing and purifying, the yarn cake is centrifugally wrung in an undersized bucket which supports substantially the entire exterior of the cake at substantially higher speed than is used for washing and purifying and then is dried in the usual manner.

The above-described process is capable of producing yarn of improved uniformity from outside to inside of the bucket cake but there still remains certain undesirable features. For example, the deformation of the relatively dry cake causes damage to the yarns and filaments therein. A freshly doffed cake of Viscose rayon is quite compact and contains only about 100% coagulating bath :based on the dry Weight of the yarn, whereas a cake well wet out with bath or Water will contain upwards of 300% thereof based on the dry Weight of the yarn. This bath is usually made up of high concentrations of salt, such as sodium sulfate, and it does not take much evaporation of water from the cake to supersaturate the solution in the cake and thus cause crystallization of the salt between the yarn layers and filaments, especially near the outer exposed surfaces. When such cakes containing only about 100% aqueous bath are mechanically deformed in any way to reduce their diameter of the order of 4%, very substantial forces must be exerted and these forces produce irreparable damage to the yarn especially when crystals exist between filaments and yarn layers.

The answer to this problem would appear obvious: simply shower the cake with water or aqueous liquid. By so doing, crystallization of the salt would be retarded, if not completely eliminated, and at the same time a lubricant would be provided between the filaments and 3 Claims. (Cl. 8-155.1)

yarn layers so that there would be less scufling and abrading action between yarns and filaments due to forces of deforming the cake. It is indeed surprising that this apparent, simple and direct approach to the problem involves unexpected difficulties. The time needed to suitably soften cakes by showering with water and aqueous solutions are surprisingly long and varied as much as tenfold from one method and solution to another. Most important, undesirable luster variations result from some treatments rendering the yarn unfit for commercial use.

It is, therefore, an object of this invention to provide an improved process for centrifugally washing and purifying bucket cakes of viscose rayon. Another object of this invention is to provide a suitable pretreatment for acid cakes of viscose rayon prior to deforming them and reducing their diameter, which pretreatment does not introduce variation in the yarn luster and is efiicient and economical in terms of time and aqueous liquid consumption. Other objects will be apparent from the description that follows.

The objects of this invention are accomplished by wetting the acid cake after it is doifed from the spinning bucket with water applied under such conditions that the cake is wetted through and a relatively high concentration of inorganic salt is maintained in the liquid within the cake. The concentration of inorganic salt in the liquid phase of the acid cake as dolled Will normally be in the range of from 25-35% and if the wetting of the cake is done so that this concentration does not go below 5% and preferably to not less than about 8%, the luster of the finished yarn is entirely satisfactory. The salt concentration is maintained within the cake from 5% to 30%.

The concentration is determined by reeling 3,000 yard skeins from the cake and measuring the salt content thereof. The cake outside is the most critical portion where the minimum allowable concentration must be maintained. The wetting of the cakes is done by dunking in water.

In copending application of Millhiser Serial No. 87,581, it is disclosed that aqueous liquids can be used such as solutions of inorganic salts or aqueous solutions of organic materials. By the present invention, it has been found that water alone will work and this affords substantial economy. The water is heated from room temperature to about C. or higher.

thereon for 30 minutes or more is reduced in concentration of bath ingredients to about 3.03.5% with a very noticeable increase in yarn luster in this section. This luster change creates sufficient non-uniformity in the yarn to bar it from commercial acceptance. Yet, on the other hand, if the cake is immersed in water for from 8 to 10 minutes the yarn on the outside is not noticeably changed in luster and satisfactory cake softening results. Samples (3,000 yards) taken from the outside of the cake showed salt concentrations of from about 6.5%7.5%. It seems that the salt solution imbibed by the yarn in the outer layers is not eliminated but remains in somewhat diluted form whereas when the cake is showered (and this method requires a relatively long time to reach the desired degree of impregnation), the outside layers of yarn are washed substantially free of salt while the rest of the cake holds solution of high salt concentration.

To further illustrate this invention the following specific examples are given.

Example I A 2.7 lb. cake of BOO-denier SO-filament bright viscose rayon yarn spun in a bucket having a bottom diameter of 7.35 inches, a depth of 7.50 inches and a 2 taper outwardly from the bottom to the top was wrapped in a protective covering aft-er dofiing and then soaked by immersion for 10 minutes in water at 30 C. The water soaked cake was deformed by means of a fourarm Topham deforming device (see U. S. 1,736,681) and then placed in a deep, perforated bucket having a bottom diameter of 7.15 inches and a 1 /2 taper outwardly from the bottom to the top. The drainage holes were arranged as a single row of 8 evenly spaced holes A; inch up from the inside bottom of the bucket. The cake was washed and purified in the revolving bucket at a speed of 1300 R. P. M. with the following cycles:

Preliminary wash.-9 minutes, 0.06% sodium bicarbonate, 35 C.

Desuljuring.9 minutes, 0.35% sodium carbonate, 0.15% sodium sulfide, 0.015% sodium cyanide, 0.05% silica, 90 C.

Intermediate wash.9 minutes,

35 C. inish.-- minutes with an aqueous emulsion of sulphated vegetable oil and mineral oil at 50 C.

All solutions were applied at a flow of about two gallons per minute to the inside of the cake using a suitable nozzle to insure uniform application over the whole of the cake structure. The cake was wrung in the same bucket used for washing and purification at 3900 R. P. M. for 90 seconds and then removed from the bucket and dried. Without soaking this large cake requires a pressure of 85 lbs. to collapse it. Ten minutes water soaking while maintaining a concentration of bath ingredients in the outer 8,000 yard layer of yarn at about 6.5% reduces this necessary pressure to less than 40 lbs.

Example II By constructing a liquid retaining vessel around the Topham four-arm collapsing device and simultaneously subjecting the cake to a constant deforming pressure of 40 lbs. while it is immersed in water, it was found possible to collapse the 2.7 lb. cake, of Example I completely in about soft water,

2 minutes. Thereafter, it was further processed as described in the previous examples.

The yarns so obtained in Examples I and II were of uniformly high quality with no noticeable dye junctions or luster variations resulting when the inside yarn from any of the treated bucket cakes was used in a fabric alongside yarn from the outside of the same cake or the outside of a different cake from the same lot processed in the same manner. A high percentage of A grade yarn cones was obtained. This signifies that no yarn degradation resulted from processing cakes in the manner above-described.

In the examples the cakes are wrapped in a protective wrapper which is permeable such as a loosely knit wrapper. While this is unnecessary, it is preferred since the yarn is protected from physical damage.

Collapsing is necessary in order to get cakes into the undersized bucket. Any method of breaking the cake structure to reduce its overall periphery will accomplish this purpose. Topham collapsing has been used merely because it is well-known and has proved adequate. Collapsing may be accomplished after soaking or may to good advantage be done during soaking. In the latter case the soaking cycle required to obtain low collapsing pressure is greatly reduced. The time of treatment will vary, but, in general, periods in the order of one hour are suificient for most purposes. In most of the tests fourarm collapsing was used. Some tests employed eight-arm collapsing with the intent of reducing the strain at any one point, and the cakes so treated were also satisfactory, although not significantly different from those collapsed with four arms. Generally, multipoint collapsing with any suitable arrangement of a plurality of arms such as 4, 8, 12, 16 or more may be used with good results.

Any departure from the above description which conforms to the present invention is intended to be included within the scope of the claims.

I claim:

1. A process for producing high quality viscose yarn of uniform luster which comprises immersing a bucket cake of viscose yarn in water until the cake absorbs about 300% by weight of water based on the dry weight of the yarn, while maintaining the salt concentration within said cake at least at 5%; thereafter multipoint collapsing the said cake to reduce its overall periphery; and centrifugally washing the collapsed cake while supporting substantially its entire exterior.

2. A process in accordance with claim 1 in which the cake is immersed in water for about ten minutes.

3. A process in accordance with claim 1 wherein the multipoint collapsing is accomplished during the immersion.

EDWARD DOUD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,736,681 Topham Nov. 19, 1929 2,042,529 Huttinger June 2, 1936 2,058,576 Dulken Oct. 27, 1936 2,101,361 Borzykowski Dec. 7, 1937 2,130,791 Dunham Sept. 20, 1938 2,243,000 Brown May 20, 1941 

1. A PROCESS FOR PRODUCING HIGH QUALITY VISCOSE YARN OF UNIFORM LUSTER WHICH COMPRISES IMMERSING A BUCKET CAKE OF VISCOSE YARN IN WATER UNTIL THE CAKE ABSORBS ABOUT 300% BY WEIGHT OF WATER BASED ON THE DRY WEIGHT OF THE YARN, WHILE MAIN TAINING THE SALT CONCENTRATION WITHIN SAID CAKE AT LEAST AT 5%; THEREAFTER MULTIPOINT COLLAPSING THE SAID CAKE TO REDUCE ITS OVERALL PERIPHERY; AND CENTRIFUGALLY WASHING THE COLLAPSED CAKE WHILE SUPPORTING SUBSTANTIALLY ITS ENTIRE EXTERIOR. 